When ordering commercial aircraft, airline companies often specify a number of design options to the manufacturer, including passenger seating layouts. The manufacturing and inventory costs associated with providing different seating arrangements and spacing between seats can be significant. These costs will become more important to the next generation of aircraft, which will offer new personal entertainment and service facilities to each passenger. Designers of such facilities are planning to install an entertainment system and passenger service system in the back of each aircraft seat for use by the passenger in the following seat. In order to communicate with these facilities, conventional wiring techniques typically require that each different seating arrangement that an airline company specifies have a different length communication lead harness. The costs and weight penalty associated with providing communication for each seat using conventional wiring techniques is likely to be unacceptable to most passenger carriers. In addition to unacceptable costs in terms of weight, conventional wiring techniques inhibit the ability to rearrange classes of seating (by sliding seats to change seating pitch) in order to maximize the payload return on a flight (even within thirty minutes of departure). The ability to rearrange classes of seating on a short-term basis is a profitable feature that is desired by most airlines.
An alternative to wiring each seat to a central communication source utilizing a conventional wire lead harness is disclosed in commonly assigned U.S. Pat. No. 4,428,078 (C. Kuo). This patent discloses what is referred to therein as a "wireless" system for communicating with a plurality of multiple-turn coupler coils disposed in the base of seats throughout an aircraft cabin. Perhaps this technology could more accurately be described as a "connectorless" transmission system, because communication signals are inductively coupled from a transmission line that is disposed in the floor of an aircraft cabin to coupler coils attached to each seat group. The communication signals are used to communicate with the passenger entertainment and service systems installed in the seats. This wireless system permits seats to be moved about in different arrangements as required by individual airlines, without concern for providing different length interconnecting wire harnesses.
In order for a connectorless communication system to be practical in an aircraft environment, the system must meet certain criteria. First, the system must be broadband, i.e., operate over a relatively broad bandwidth. Second, the system must be duplex, i.e., have the capability of transmitting and receiving in both directions from a central unit to a plurality of remote (seat) units. Further, the system must be highly efficient, low in weight, and highly reliable.
The development of higher quality entertainment and services for aircraft passengers creates the broad bandwidth requirement. Present and future aircraft entertainment systems provide video as well as audio entertainment. Video entertainment requires 6 MHz per channel and contemporary FM stereo requires 200 KHz per channel. Service data transmission requires a bandwidth of 100 KHz per 50 K bit/second channel. Duplex communication is required because it is necessary to be able to establish two-way communication between the seats of an aircraft and central control equipment in order for a passenger to initiate action, such as tuning on a TV mounted in the seat in front of the passenger, and the action to occur.
High efficiency is required because it is necessary to communicate broadband RF signals throughout an aircraft cabin without interfering with other electronic equipment such as the navigational equipment and computer systems of the aircraft. It is also necessary that the system operate with minimal interference from outside sources. More specifically, conventional RF transmitting systems use a high-powered signal to excite an antenna. Transmitter power is proportional to the square of the distance between the transmitting antenna and the receiving antenna. The use of high power creates a potential interference problem with other electronic systems that operate in the same area. Conversely, a broadband receiving antenna tends to pick up interfering signals generated by other signal sources. Thus, to be practical a system for use onboard an aircraft must operate with minimal power and have a minimal tendency to pick up interference from external sources.
The present invention is directed to providing a highly efficient, broadband, inductively coupled, duplex, RF transmission system suitable for use in the passenger compartment of aircraft to communicate between a central unit and a plurality of remote seat units.